In a recording/playback apparatus (for example, a CD-RW drive), when recording or playing back content on or from a disc, it is demanded for protecting the content that recording/playback operations be correctly controlled and unauthorized copying be prevented.
For example, published Japanese translations of PCT international publication for patent application No. 2002-521789 discloses that data is recorded or played back on or from discs by using a data format consisting of user data and user control data.
In such a data format, the user data is recorded after being encrypted with a key by using the disc ID unique to a disc, thereby protecting content from unauthorized copying.
Japanese Unexamined Patent Application Publication No. 2002-84271 discloses a recording/playback apparatus 1 shown in FIG. 1.
In the example shown in FIG. 1, the recording/playback apparatus 1 is formed of a drive 11 an AV board 12, and a dedicated bus 13. The drive 11 includes a recording/playback processor 21, and the AV board 12 includes an AV content processor 31, a content protector 32, an input unit 33, and an output unit 34.
When an optical disc 41 is loaded, the recording/playback processor 21 obtains the disc ID and RKB (Renewal Key Block) unique to the optical disc 41, and supplies them to the content protector 32 of the AV board 12 via the dedicated bus 13. The content protector 32 generates a key by using a disc key obtained from the disc ID and RKB, and stores the generated key.
The AV content processor 31 supplies content with a copyright (i.e., such content should be protected) received via the input unit 33, for example, an antenna, to the content protector 32. The content protector 32 encrypts the content with the prestored key by using the disc key obtained from the disc ID and RKB, and supplies the encrypted content to the recording/playback processor 21 via the dedicated bus 13 as the content to be protected. The recording/playback processor 21 receives the encrypted content and records it on the optical disc 41.
The recording/playback processor 21 also plays back predetermined encrypted content from the optical disc 41, and supplies the content to the content protector 32 via the dedicated bus 13. The content protector 32 decrypts the encrypted content with a key by using the disc key obtained from the disc ID and RKB, and supplies the content to the AV content processor 31. The AV content processor 31 decodes the decrypted content according to, for example, an MPEG (Moving Picture Experts Group) and plays back the content. The output unit 34 outputs the played back content.
As described above, since data is sent and received between the drive 11 and the AV board 12 via the dedicated bus 13 in the recording/playback apparatus 1, content can be protected from external access by using the disc ID or RKB.
As a modified example of the recording/playback apparatus 1 shown in FIG. 1, a recording/playback apparatus 51 shown in FIG. 2 can be considered. In FIG. 2, the elements corresponding to the elements shown in FIG. 1 are designated with like reference numerals, and an explanation thereof is thus omitted. In the example shown in FIG. 2, the drive 11 and the AV board 12 are separated via a bus 61 (general-purpose bus) (for example, they are separated by a household LAN (Local Area Network)).
Accordingly, in the example shown in FIG. 2, since the disc ID and RKB are directly sent to the bus 61, there is a possibility of the disc ID and RKB being stolen. For example, when connecting an HDD (Hard Disk Drive) 71 to the bus 61 for recording content, the “disc ID”, “RKB”, and “content encrypted with a disc key obtained from the disc ID and the RKB” on the bus 61 are sent (monitored) and copied into the HDD 71.
In the example shown in FIG. 2, in the HDD 71, a 16-B disc ID, a several-MB RKB, 20-GB encrypted content, and a several-KB program which are sent to the HDD 71 as described above are stored. If the “disc ID”, “RKB”, and “content encrypted with the disc key obtained from the disc ID and RKB” are supplied to the AV board 12 from the HDD 71, the AV board disadvantageously plays back the content since it cannot distinguish them from those played back by the authorized optical disc 41.
A “spoofing drive” or a “spoofing program”, which supplies the “disc ID”, “RKB”, and “content encrypted with the disc key obtained from the disc ID and RKB” to the AV board 12 may be disadvantageously distributed as a general playback execution apparatus or program.
Accordingly, in the recording/playback apparatus 51 in which the drive 11 and the AV board 12 are separated from each other via the bus 61, data may be distributed, not only to authorized discs, but also to unauthorized media, for example, the HDD 71.
Accordingly, a recording/playback apparatus 81 which conducts mutual authentication, such as that shown in FIG. 3, has been proposed. In the example shown in FIG. 3, a mutual authentication unit 91 is provided for the drive 11, and a mutual authentication unit 92 is provided for the AV board 12. By conducting mutual authentication processing between the two mutual authentication units 91 and 92, content can be sent and received by being encrypted with a common key shared by the drive 11 and the AV board 12.
Accordingly, in the HDD 71 without a mutual authentication function and compatible with optical discs recorded by the recording/playback 1 or 51, even if the “disc ID”, “RKB”, and “content encrypted with the disc key obtained from the disc ID and RKB” are copied, they cannot be decrypted, thereby making copying substantially impossible in the HDD 71. Thus, the above-described “spoofing drive” or “spoofing program” can be prevented.
Recently, however, for superdistribution in which encrypted content is provided free of charge, or for storing content in a PC (Personal Computer), it is demanded that content that does not have to be protected can be recorded or played back without being encrypted on the bus 13 so as to allow the user to copy such content. On the other hand, it is also demanded that content that should be protected be prevented from being copied.
At present, however, since the HDD 71 of an ordinary PC is not provided with a mutual authentication function, in the recording/playback apparatus 81, not only specific content to be protected, but also content that does not have to be protected but to be stored in a PC, cannot be copied.